The present invention relates to a device for implanting a microphone and at least a first pressure compensating member in a telephone watch enclosed in a case, this microphone being covered with an impermeable membrane and this first pressure compensating member including a hydrophobic disc, said membrane and said disc being in direct communication with the exterior of the telephone watch.
When a microphone and earpiece are implanted in a watch to make it into a telephone watch, the problem of the watch's watertightness arises when it is immersed at a certain depth, a depth limit being generally fixed at thirty meters. The problem of balancing the pressures existing outside and inside the watch also arises when the latter is brought to different altitudes. Immersion and atmospheric pressure are constraints which do not pose major difficulties when dealing with a simple watch, but which however raise questions when this watch is associated with acoustic transducers which are subjected to the same constraints. It will also be mentioned that in a telephone watch, the microphone and earpiece are very close to each other and that measures have to be taken to prevent an internal acoustic feedback.
The aforecited problems have found solutions which are disclosed in European Patent No. 0 899 634 A.
In particular, this document discloses a membrane able to be deformed which covers a microphone. This membrane separates the microphone from an inlet cavity arranged in the watch case, this cavity being in direct communication with the exterior of the watch. Between the membrane and the microphone there is arranged an intermediate space allowing the membrane to be deformed by the action of external static pressure, immersion in water, for example. Deformation of the membrane is however limited, on the microphone side, by a support member. Out of a liquid, the membrane is mounted so as to be able to vibrate freely via the action of the acoustic energy to be received by the microphone. The problem of the microphone's watertightness when immersed is thus resolved while assuring that it operates properly in the open air.
The aforecited document also discloses a hydrophobic disc forming the essential part of a first pressure compensating member between the outside and inside of the watch. This disc must of course be impermeable to liquids, for example when the watch is immersed. This disc must also be permeable to gases whose pressure varies slowly, in order to insulate the air in front of the earpiece (disclosed in European Patent No. 0 899 635 A) from the air behind said earpiece and thus preventing acoustic short-circuiting leading to poor efficiency of the transducer. In practice, this disc constitutes a low pass filter only allowing pressure variations of gases such as air, of very low frequency, typically {fraction (1/10)} of a Hz and less, to pass. In order to satisfy the conditions imposed, the disc may for example be made of sintered Teflon (registered trademark) or ceramics.
The same document discloses finally a second pressure compensating member located in proximity to the microphone and in communication on the one hand with the space arranged between this microphone and the deformable membrane which covers it and on the other hand with the inside of the watch. This second member is formed essentially of a similar disc to that described in the preceding paragraph. It will be understood that this disc allows, in particular the microphone to be acoustically insulated from the earpiece because it only allows airs to pass, the pressure of which varies slowly, and thus prevents the aforementioned acoustic feedback. Here however, the hydrophobic quality of the disc is not used since the latter is not in contact with a liquid medium. It will be understood however that in order to simplify things, the same material as that used for the disc fitted to the first pressure compensating member is used.